High-intensity interval training, also known as HIIT, involves short bouts of extreme effort alternated with periods of rest.

"HIIT workouts are quick and dirty, never lasting more than 30 minutes including a warm-up and short cool-down," explains Gina Harney, certified personal trainer and creator of Fitnessista.com. "You're working as hard as possible for a short amount of time and then reaping the rewards throughout the day."

While there's no such thing as a fitness miracle, HIIT workouts come pretty close.

Complete 3 rounds of circuit 1, then rest for 30 seconds to 1 minute. Boost your heart rate again by running or walking 1/4 mile. Then complete 3 rounds of circuit 2, followed by a cool-down stretch and you're done.

Hold a set of dumbbells and create 90-degree angles with each arm so upper arms are parallel to the ground and dumbbells are at about head height. As you exhale, press the weights overhead without clanking the weights together. Return to the starting position, not letting elbows droop below shoulder height to keep some resistance.

12 reps

Lie faceup on a mat. Bring elbows out in line with shoulders to create a 90-degree angle. Press the weights up without clanking them together, focusing on engaging the muscles in your chest. Lower weights back to the starting position.

Start in a side plank (either full or modified by keeping your bottom knee on the floor) and hold a light dumbbell in your top hand. Bring weight in front of the center of your core. Keeping your arm slightly bent, lift weight up to shoulder height. Return to starting position. For even more of a challenge, you can lift your top leg and touch it to the weight between each rep.

Start in plank position with hands planted directly under shoulders (slightly wider than shoulder-width apart). Ground your toes into the floor to stabilize the bottom half of your body. Keeping your spine straight (don't lift hips, and keep neck in line with your spine instead of dropping it forward) and knuckles pressing into the floor, lower your body until your chest almost grazes the floor. Exhale as you press back up.

You can perform these on a bench (hands on the bench, feet on the floor) or on the floor. Point your fingertips toward your toes and bend your elbows, making sure to keep your hips lifted. Straighten your arms by engaging your triceps. For an added challenge, straighten your legs, balance on only one leg, or place a flat weight on your lap.